Smoke detector



Jan. 25, 1966 Q w. M. HAESSLER ETAL 3,231,748

SMOKE DETECTOR Filed-Oct. 30, 1961 5 Sheets-Sheet l INVENTORS M4175? M $155191 :1?

ATTORNEY Jan. 25, 1966 Filed 00;. 30, 1961 w. M. HAESSLER ETAL SMOKE DETECTOR 5 Sheets-Sheet 2 ATTORNEY 1966 w. M. HAESSLER ET AL 3,231,748

SMOKE DETECTOR Filed Oct. 30, 1961 5 Sheets-Sheet 3 MEL/M444 4 AT ORNEY Jan. 25, 1966 Filed Oct. 30, 1961 w. M. HAESSLER ET AL 3,231,748

SMOKE DETECTOR 5 Sheets-Sheet 5 AT ORNEY United States Patent I The present invention relates to apparatus for detecting the presence of suspended matter in fluids, such as smoke in air or the like, and more particularly relates to a smoke detector which is suitable to detect the presence of smoke in the air in each of a plurality of spaces such as the compartments and holds of a ship, or rooms in a building. a 1

Smoke usually refers to a gaseous dispersion system consisting of particles oflow vapor pressure produced as a result of incomplete combustion processes including solid carbon particles and minute droplets of high molecular weight carbonaceous matter destructively distilled due to the heat of combustion. The smoke particles, in most instances, are, for some time after generation, very .small, ranging from approximately 01 to, 1.0 micron in diameter, (A micron= meters.)

Smoke is quite unstable. Under the influence of a live- .ly Brownian motion, the particles in a cloud of smoke collide with each other and agglomerate. This process goes on continuously until the number of particles has been considerably diminished and the average size very largely increased. The mass concentration of relatively stable smokes is usually low and in the majority of cases is below a gram per cubic meter.

The formation of smokes is a dynamic process involving a flow of vapors and particles in the presence of the intervening gaseous medium. The subsequent history of the smoke, whether in a still or a moving gaseous medium, is dependent upon diffusion, sedimentation, and coagulation of particles, with the added effects of condensation of water vapor due to temperature reductions. Combustion processes always release water vapor and, in the subsequent cooling down of initial combustion, condensation nuclei develop about individual smoke particles rendering them larger in size, slower in pace, hence, furtheringultimate sedimentation.

An excellent example of this action can be seen in the case of a lighted cigarette, wherein the smoke rising from the burning end is hot and bluish, indicating small size smoke particles, while the smoke issuing forth from the mouth end is grayish, having been cooled in transit through the unburning tobacco wherein a condensationoccurred.

The enlarged size of the smoke particles from the mouth end of the cigarette gives the smoke a less bluish hue and a more grayish appearance. Furthermore, when the smoker inhales and subsequently exhales, the smoke cloud becomes even whiter, indicating further enlargement of the particles due to further condensation of the moisture coming from the smokers respiratory system.

Smoke particles, as initially formed, are usually in the order of .01 to 0.1 micron in diameter and thus have a diameter less than the wave length of visible light. Since smoke particles are of this size, they cannot be optically resolved as a definite object, but, rather, give an illusory evidence of their existence through the optical means of light scattering.

It has long'been known that a beam of light passing through a clear liquid or gas does not become visible to the eye, but if dispersed particles are present, the path becomes clearly marked. This is known as the Tyndall effect. A familiar example is the visible path of the light beam from a projection lantern towards the screen, the

ticles in the air. If the beam of light is brought to a focus, a bright cone called the Tyndall cone is obtained. The light is scattered in all directions by the very small particles dispersed therein even though they are too small (less than the wave length of, the incident light) to reflect thelight in the usual manner. Instead, a diffraction phenomenon occurs, wherein each of the very small particles produces new elementary spherical waves. The particles behave as if they were individual point sources of light radiating in all directions. Hence, part of the light energy is drained off and scattered, thereby reducing the intensity along the original path.

The distribution of the scattered light varies considerably as the angle of observation is changed with respect to the path of incident light. For smoke particles in the range of .3 micron in diameter and having a refractive index of 1.5, the intensity of scattered light in a forward direction will be about 20 times that scattered in a rearward direction, and about 12 times that scattered in. a directionat right angles to the incident light beam. The conditions resulting in the scattering are 1 extremely complex, and for very small particles with radii of less than about 0.1 micron in length, the wavelength of the incident light scattering is proportional to the square of the volume of the particle, inversely proportional to the fourth power of the wavelength of the non-scattered light and proportional to a factor involving the difference in the index of refraction between the particle and the medium in which it is suspended.

There are a number of methods by which smoke can be detected among which are those using the reflection of light principle as disclosed in U.S.,Patent No. 1,828,- 894, those using'the fobscuration of light principle, as

- used in instrument standards for the determination of the visibility being produced by cigarette smoke and dust parpercent smoke in mediums, and those using a combination of these principles as disclosed in U.S. Patent No. 2,301,367.

In all of these constructions a source of light is used to 1 project a light beam'through a chamber through which air to be testedfor smoke is passed, the presence of smoke causing variations in the output of a photoelectric element. By reason of their construction the prior devices .haverequired a comparatively high wattage in order to utilized one source of light for a plurality of detectors by placing the. detectors in a radial arrangement around the source of light.

In other constructions, the air to be tested for smoke has been withdrawn from the plurality of individual areas to be protected and successively passed through a single smoke detector. This construction has not been wholly satisfactory in that the air from only one area is tested at a time and purging of the detector chamber is necessary before another sample is introduced.

It has been found that the detection of smoke by the obscuration method is very marginal when the smoke concentration is of the order of 2% when measured as the-obscuration occurring in a one foot long tube. The sensitivity of obscuration detectors is increased if a longer path length is used either "by increasing the length of the smoke chamber of the detector, which results in an unwieldy device, or by the use of multiple reflections through the use of mirrors so that the light is caused to pass through the smoke in a plurality of paths in a zigzag fashion. In such a construction the sensitivity obviously is dependent upon the cleanliness of the mirror surfaces in the smoke chamber.

The present invention aims to overcome the foregoing ditficulties and disadvantages by providing a smoke detector which is practical for the testing of air for smoke from a plurality of spaces simultaneously, and which is of low wattage.

In accordance with the invention this is accomplished by providing a smoke detector in which the photo-electric element is directed towards the source of light, means being provided blocking direct rays of light from the photo-electric element, the presence of smoke producing forward light scatter which is used to provide a signal by causing variations in the output of a photo-electric element.

Another object of the invention is to provide a smoke detector which is simple and economical in manufacture, eflicient in operation and durable in use.

Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings which show, by way of examples, embodiments of the invention.

In the drawings,

FIGURE 1 is a schematic sectional view of a smoke detector in accordance with the invention.

FIGURE 2 is a schematic sectional view of a somewhat modified construction in accordance with the invention.

FIGURE 3 is a still further modified construction in accordance with the invention.

FIGURE 4 is a sectional view of a commercial embodiment in accordance with the invention and corresponding to the construction shown in FIGURE 3.

FIGURE 5 is a front view of the construction shown in FIGURE 4 as viewed from the right hand side thereof.

FIGURE 6 is a back view of the construction shown in FIGURE 4 as viewed from the left hand side thereof.

FIGURE 7 is a polar graph showing the intensity of scattered light as a function of the angle thereof with respect to the source.

FIGURE 8 is a rectilinear graph corresponding to the polar graph of FIGURE 7.

FIGURE 9 is a graph showing the sensitivity of the present construction as compared to prior constructions.

Referring to the drawings there is shown in FIGURE 1 a smoke detector 1 in accordance with the invention and including a housing 2 having a light source 4 at one end thereof and a photoelectric element 5 at the other end thereof. A partition 6 is apertured as indicated at 7 and a smoke inlet 9 and a smoke outlet 10 are provided to pass air through space 11 in the housing 2. A suitable lens system 12 is provided to direct light from the source 4 through the aperture 7 and through another lens system 14 to the photo-electric element 5. The aperture 7 is positioned at a common focus point for both lens systems. Light beam angle restricting means 15 are positioned so as to block direct rays of light emitted from the source 4 from reaching the photo-electric element 5. The region of dark space is indicated by the numerals 16 and 17. The light spaces are indicated by the numerals 19 and 20.

In the operation of this embodiment air tobe tested for smoke is passed into the smoke detector through its inlet 9, through the aperture 7 in the partition 6, and exhausted through the smoke outlet 10. In the event there were no particles whatsoever in the air its passage through the aperture 7 would cause no light to impinge on the photo-electric element 5 inasmuch as the direct rays of light from the source 4 have been stopped by the light beam angle restricting member 15. However, in the event of the presence of smoke in the air a portion of the forward scattered light will impinge on the photocell 5' which maybe connected in a suitable circuit in a conventional manner to provide an alarm or a visual indication of the percentage of smoke present. The smoke detector 27 shown in FIGURE 2 differs from that shown in FIGURE 1 in that instead of providing light beam angle restricting means such as the member 15 of FIGURE 1, an equivalent light beam angle restricting means is provided by a partition 28 having an aperture 29 therein which provides a cone of light focusing at a point 31 so that no direct rays of light impinge upon the photo-electric element 5. However, in the presence of smoke particles in the, air being tested, by reason of the forward scattering of the light, it is directed tothe photoelectric element 5 to provide an alarm in the usual manner.

In FIGURE 3 there is shown a schematic drawing of a commercial embodiment of they smoke detector more fully illustrated in the FIGURES 4-6. Smoke detector 34 utilizes a tubular member 35 instead of the apertured partition 28 of FIGURE 2 to restrict the beam of light emitted by the source 4. The tubular member 35 is positioned along a line running from the light source 4 to the aperture 7. In addition, the right hand end of the smoke detector 34 is provided with a viewing window 36 which provides a means of ascertaining whether or not the light source 4 is emitting light.

At the upper end of the smoke detector 34 is another viewing window 37 positioned at an angle of with respect to the axis of the light beam passing through the tubular member 35. The window 37 provides a means for the visual detection of smoke, there being no light visible through the window 37 unless the beam of light is forwardly scattered by smoke particles passing through the aperture 7. On the lower edge of the smoke detector 34 is positioned a photoelectric element chamber 38 in which is positioned the photoelectric element 5 having the lens 14 so positioned that the photoelectric element 5 views the aperture 7 at an angle of 150 from the light emitting through the beam 35. Thus the presence of smoke in the aperture 7 may be detected by the photoelectric element 5 in the same manner as the smoke may be visually detected through the window 37.

Referring to FIGURES 4, 5 and 6 there is shown a smoke detector 40 which is a commercial embodiment of the invent-ion. In this construction the light source 4 is an incandescent lamp and the photoelectric element 5 is a RCA type 931A multiplier photo tube. The partition 6 is provided with an aperture 7 as heretofore described. The inlet 9 and outlet 10 are positioned on the left hand lower side of the housing, the outlet 10 being in front of the inlet 9 which extends across the inner surface of the housing discharging into the housing on the right of the partition 7 so that the air to be tested for smoke must pass through the aperture 7 and then through the open top portion of the outlet 10 to be exhausted from the housing. The outer ends of both the inlet 9 and the outlet 10 are made in the form of quick release couplings so that the housing may be positioned in a modular arrangement with other housings.

The lens 12 is adapted to focus the beam of light emitted by the source 4 towards the aperture 7. In order to permit accurate focusing of the light source at the aperture 7, a translucent member 41 is swung across the aperture by positioning it at the end of a spring restrained rod 42 which is turned by engaging its outer end with a screwdriver. When the light source 4 is properly focused the image of its filament is centrally projected on the translucent member 41. The lens 14 is adapted to receive light from the direction of the aperture 7 and focus the light on the sensitive portion of the phototube 5.

The viewing window 36 of FIGURE 4 has positioned behind it a vane member 43 carried at its upper end by a plug member 44 secured in the housing in any suitable manner. The vane member 43 is light in weight and is adapted to continually vibrate or swing when air is discharged from the end of the inlet 9 indicated by dotted lines.

The smoke detector 40 is made in modular form so that an individual smoke detector may be used for each stalled in drawers of a suitable frame construction wherein the smoke detector is slid in from the front, a handle 45 being used to'facilitate the insertion and re moval of the unit. When inposition the module is secured by quick fastening studs 46 and 47. A trouble lamp 49 and a smoke alarm lamp 50 are positioned on the front end of the smoke detector as shown in FIG- URE 5. Adjustment means for potentiometers used in the electrical circuit are shown at 51, the potentiometers being indicated by the numerals 52. An electrical component assembly 54 and electrical connecting means 55 are positioned towards the rear end of the housing. Side walls 56 and 57 are secured to the main portion of the housing by screws as indicated at 59.

In order that the light source 4 may be accurately focused upon the aperture 7, aprefocused lamp is used and held in position by prongs 60, the lamp being supported by a bracket 61 having a base plate 62 secured in position by screws 64. Additional adjustment of the filament of the prefocused lamp is obtained by means of a screw member 65 holding in position an adjustment washer 66 positioned over an oversize hole in downwardly depending portion 67 of the bracket member 61.

FIGURE 7 is a polar graph showing the variation in intensity of scattered light plotted with respect to the angle of the source, and a corresponding curve plotted in rectangular coordinates is shown on FIGURE 8. Referring to FIGURE 7 it will be noted that the intensity of the scattered light 70 is at a maximum at 180 from the source of light and at that location is many times greater than at 90 from the source of light. Curve 71 of FIGURE 8 illustrates the variation in intensity with angular position more emphatically. The curves of FIGURES 7 and 8 illustrate the intensity of the scattered light only and do not take into consideration the decrease in the intensity of the light caused by the obscuration effect of smoke particles interposed between the source of light and the viewing position.

Referring to FIGURE 9 there is plotted curves showing the relationship of the photoelectric element output for the obscuration type smoke detector and for constructions in accordance with the present invention. In the obscuration type smoke detector the light impinges directly on the photoelectric element and thus the photoelectric element output is at a maximum when no smoke is present. The photoelectric element output curve of the obscuration type smoke detector is indicated as curve 72.

In the smoke detector according to the present invention the output of the photoelectric element is at a minimum when no smoke is present, the curve being indicated as 74 for the construction of FIGURE 1.

It should be noted that the variation in output for the construction of the 180 forward light scatter type of smoke detector of FIGURE 1 is considerably greater than the variation in the output of the obscuration type smoke detector. For ten percent smoke, the forward light scatter detector photoelectric element increases its output 135 percent, while the obscuration type detector photoelectric element output is reduced only ten percent for the same amount of smoke.

The output of the photoelectric element for the constructions of FIGURES 2-6 in which the angle of forward scatter is 150 degrees as shown by curve 75, and for a 90 degree position by the curve 76.

While the invention has been described and illustrated with reference to specific embodiments thereof, it will be understood that other embodiments may be resorted to without departing from the invention. For example, the positions of the source of light and of the photoelectric elements may be varied and mirrors or other reflecting surfaces used to accomplish the results of the present constructions. Therefore, the forms of the invention set out above should be considered as illustrative and not as limiting the scope of the following claims.

We claim:

1. A forward light scatter smoke detector comprising a housing having front and rear portions, inlet and outlet means for the housing, a light chamber in the rear portion of the housing, a source of light in the light chamber, an apertured wall for the light chamber, a lens in the apertured wall of the light chamber, the lens having a focal point located within the housing, a tube in axial alignment with the lens and adapted to restrict the beam of light passing therethrough, a viewing window in the wall of the front portion of the housing in alignment with the axis of the tube for visual supervision of the light source, a movable air current flow indicator member located in the front portion adjacent the viewing window in the path of light passing through the tube, the inlet located in the front portion of the housing and directed towards the air current flow indicator, an apertured partition extending across the housing located at the focal point of the lens and positioned between the tube and the visual supervision viewing window, a translucent member positioned adjacent the apertured partition, means to move the translucent member into and away from a position intercepting the passage of the beam of light directed towards the aperture and the viewing window, the outlet located in the rear portion of the housing, means adapted to pass air to be tested for smoke from the inlet to the outlet through the aperture of the partition, a second viewing window for visual detection of smoke, and a photoelectric element, both the second viewing window and the photoelectric element positioned in the front portion of the housing at angles less than right angles with respect to the axis of said tube outwardly of the beam of light and directed in viewing position towards the aperture of the partition whereby light scattered by particles of smoke is directed towards the second viewing window and towards the photoelectric element.

2. A forward light scatter smoke detector comprising a housing having front and rear portions, inlet and outlet means for the housing, a light chamber in the rear portion of the housing, a source of light in the light chamber, an apertured wall for the light chamber, a lens in the apertured wall of the light chamber, the lens having a focal point located within the housing, a tube in axial alignment with the lens and adapted to restrict the beam of light passing therethrough, a viewing window in the wall of the front portion of the housing in alignment with the axis of the tube for visual supervision of the light source, an apertured partition extending across the housing 10- cate-d at the focal point of the lens and positioned between the tube and the visual supervision viewing window, a

translucent member positioned adjacent the apertured partition, means to move the translucent member into and away from a position intercepting the passage of the beam of light directed towards the aperture and the viewing window, means adapted to pass air to be tested for smoke from the inlet to the outlet through the aperture of the partition, a second viewing window for visual detection of smoke, and a photoelectric element, both the second viewing window and the photoelectric element positioned in the front portion of the housing at angles less than right angles with respect to the axis of said tube outwardly of the beam of light and directed in viewing position towards the aperture of the partition whereby light scattered by particles of smoke is directed towards the second viewing window and towards the photoelectric element.

3. A forward light scatter smoke detector comprising a housing having front and rear portions, inlet and outlet means for the housing, a light chamber in the rear portion of the housing, a source of light in the light chamber, an apertured wall for the light chamber, a lens in the apertured wall of the light chamber, the lens having a focal point located within the housing, a tube in axial alignment with the lens and adapted to restrict the beam of light passing therethrough, a viewing window in the wall of the front portion of the housing in alignment with the axis of the tube for visual supervision of the light source, an apertured partition extending across the housing at the focal point of the lens and positioned between the tube and the visual supervision viewing window, means adapted to pass air to be tested for smoke from the inlet to the outlet through the aperture of the partition, a second viewing window for visual detection of smoke, and a photoelectric element, both the second viewing window and the photoelectric element positioned in the front portion of the housing at angles less than right angles with respect to the axis of said tube outwardly of the beam of light and directed in viewing position towards the aperture of the partition whereby light scattered by particles of smoke is directed towards the second viewing window and towards the photoelectric element.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 6/ 1931 Germany. 5/ 1939 Germany. 3/ 1952 Great Britain. 5/ 1955 Great Britain.

NEIL C. READ, Primary Examiner. 

1. A FORWARD LIGHT SCATTER SMOKE DETECTOR COMPRISING A HOUSING HAVING FRONT AND REAR PORTIONS, INLET AND OUTLET MEANS FOR THR HOUSING, A LIGHT CHAMBER IN THE REAR PORTION OF THE HOUSING, A SOURCE OF LIGHT IN THE LIGHT CHAMBER, AN APERTURED WALL FOR THE LIGHT CHAMBER, A LENS IN THE APERTURED WALL OF THE LIGHT CHAMBER, THE LENS HAVING A FOCAL POINT LOCATED WITHIN THE HOUSING, A TUBE IN AXIAL ALIGNMENT WITH THE LENS AND ADAPTED TO RESTRICT THE BEAM OF LIGHT PASSING THERETHROUGH,A VIEWING WINDOW IN THE WALL OF THE FRONT PORTION OF THE HOUSING IN ALIGNMENT WITH THE AXIS OF THE TUBE FOR VISUAL SUPERVISION OF THE LIGHT SOURCE, A MOVABLE AIR CURRENT FLOW INDICATOR MEMBER LOCATED IN THE FRONT PORTION ADJACENT THE VIEWING WINDOW IN THE PATH OF LIGHT PASSING THROUGH THE TUBE, THE INLET LOCATED IN THE FRONT PORTION OF THE HOUSING AND DIRECTED TOWARDS THE AIR CURRENT FLOW INDICATOR, AN APERTURED PARTITION EXTENDING ACROSS THE HOUSING LOCATED AT THE FOCAL POINT OF THE LENS AND POSITIONED BETWEEN THE TUBE AND THE VISUAL SUPERVISION VIEWING WINDOW, A TRANSLUCENT MEMBER POSITIONED ADJACENT THE APERTURED PARTITION, MEANS TO MOVE THE TRANSLUCENT MEMBER INTO AND AWAY FROM A POSITION INTERCEPTING THE PASSAGE OF THE BEAM OF LIGHT DIRECTED TOWARDS THE APERTURE AND THE VIEWING WINDOW, THE OUTLET LOCATED IN THE REAR PORTION OF THE HOUSING, MEANS ADAPTED TO PASS AIR TO BE TESTED FOR SMOKE FROM THE INLET TO THE OUTLET THROUGH THE APERTURE OF THE PARTITION, A SECOND VIEWING WINDOW FOR VISUAL DETECTION OF SMOKE, AND A PHOTOELECTRIC ELEMENT, BOTH THE SECOND VIEWING WINDOW AND THE PHOTOELECTRIC ELEMENT POSITIONED IN THE FRONT PORTION OF THE HOUSING AT ANGLES LESS THAN RIGHT ANGLES WITH RESPECT TO THE AXIS OF SAID TUBE OUTWARDLY OF THE BEAM OF LIGHT AND DIRECTED IN VIEWING POSITION TOWARDS THE APERTURE OF THE PARTITION WHEREBY LIGHT SCATTERED BY PARTICLES OF SMOKE IS DIRETED TOWARDS THE SECOND VIEWING WINDOW AND TOWARDS THE PHOTOELECTRIC ELEMENT. 